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Electron Beam Technology for VOCs {short description of image}

From Ground Water Currents, January 1996, Issue No. 14

Electron Beam Technology for VOCs

By Franklin Alvarez, EPA National Risk Management Research Laboratory

EPA's Superfund Innovative Technology Evaluation (SITE) program demonstrated the High Voltage Environmental Applications, Inc. (HVEA), electron beam (E-beam) technology. The E-beam was developed to destroy semivolatile and volatile organic compounds (VOCs) in liquid wastes, including ground water, wastewater and landfill leachate. The objective of the demonstration, conducted at the U.S. Department of Energy Savannah River Site in Aiken, South Carolina, was to determine the effectiveness of the E-beam for treating ground water contaminated with VOCs.

The E-beam system treated about 70,000 gallons of ground water. The principal contaminants were trichloroethene (TCE) and tetrachloroethene (PCE), which were present at concentrations of about 27,000 and 11,000 micrograms per liter (ug/L), respectively. The ground water also contained low levels (40 ug/L) of cis-1, 2-dichloroethene (1,2-DCE). Removal efficiencies were greater than 99% for TCE and PCE and 91% for 1,2-DCE.

During a portion of the demonstration, the groundwater was spiked with 1,2 dichloroethane (1,2-DCA); 1,1,1-trichloroethane (1,1,1-TCA); chloroform; carbon tetrachloride (CCl4); and aromatic VOCs, including the BTEX compounds benzene, toluene, ethylbenzene and xylenes. The influent concentrations of these spiking compounds ranged from 100 to 500 ug/L. These compounds were chosen either because they are relatively difficult to remove using technologies that employ free radical chemistry such as the E-beam does (i.e., 1,2-DCA, 1,1,1-TCA, chloroform and CCl4) or because they are common ground water contaminants (i.e., BTEX). Removal efficiencies ranged from 68% to 98% for the chlorinated compounds and from 96% to 98% for BTEX compounds.

The treatment system effluent met Safe Drinking Water Act (SDWA) maximum contaminant levels (MCL) for 1,2-DCE, CCl4 and BTEX at a significance level of 0.05. However, the treatment system effluent did not meet this test for the other compounds. In addition, the effluent LC50 values (the percentage effluent in the test water at which at least 50% of the test organisms died) ranged from less than 6.2 to 8% for water fleas and from 8.6 to 54% for flathead minnows.

Here's how the E-beam works. It irradiates water with a beam of high-energy electrons, causing the formation of three primary transient reactive species: aqueous electrons, hydroxyl radicals and hydrogen radicals. Target organic compounds are either mineralized or broken down into low molecular weight compounds, primarily by these species.

The HVEA E-beam and is rated for a maximum flow rate of 50 gallons per minute (GPM). The system has a strainer basket, an influent pump, the E-beam unit, a cooling air processor, a blower and a control console.

After particulates larger than 0.045 inch are removed from the influent by the strainer basket, the influent pump transfers contaminated water to the E-beam unit. This unit is made up of an electron accelerator, a scanner, a contact chamber and lead shielding. The electron accelerator is capable of generating an accelerating voltage of 500 kilovolts and a maximum beam current of about 42 milliamps, which results in a maximum power rating of 21 kilowatts. The scanner deflects the E-beam, causing the beam to scan the surface of the water as it flows through the contact chamber. The E-beam significantly heats the titanium window, which is cooled by air recirculated through the contact chamber. The air is conditioned by a cooling air processor.

E-beam dose is a key operating parameter for this technology. This is a function of several parameters, including the density and thickness of the water stream; E-beam power, which is a function of beam current and accelerating voltage; and the length of time that the water is exposed to the E-beam which depends on the flow rate.

The carbon adsorber was used to destroy ozone (O3) formed in the cooling air when exposed to the E-beam. Vapor phase VOCs not destroyed by the E-beam are removed by the carbon adsorber. Since the SITE demonstration, HVEA has replaced the carbon adsorber with an O3 destruction unit.

For more information, call Franklin Alvarez at EPA's National Risk Management Research Laboratory at 513-569-7631. Key findings will also be documented in a SITE Technology Capsule, an Innovative Technology Evaluation Report and the Technology Evaluation Report; to get on the mailing list for these reports, send a FAX to Franklin Alvarez at 513-569-7677 with your name and address.

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